Coated article with low-E coating including tin oxide interlayer for high bend applications

ABSTRACT

A coated article is provided which may be heat treated (e.g., thermally tempered) and/or heat bent in certain example instances. In certain example embodiments, an interlayer of or including a metal oxide such as tin oxide is provided under an infrared (IR) reflecting layer so as to be located between respective layers of or including silicon nitride and zinc oxide. It has been found that the use of such a tin oxide inclusive interlayer results in significantly improved bendability of the coated article in applications such as vehicle windshields with deep bends. In certain example instances, an overcoat of a material such as zirconium oxide may also be provided.

This is a continuation-in-part (CIP) of U.S. patent application Ser. No.10/797,561, filed Mar. 11, 2004, the disclosure of which is herebyincorporated herein by reference.

This invention relates to a coated article, such as a vehicle windshieldor the like, including a low-E coating. In certain example embodiments,an interlayer comprising tin oxide or the like may be provided under aninfrared (IR) reflecting layer and in particular between respectivelayers comprising silicon nitride and zinc oxide. In certain exampleembodiments, the coated article may be heat treated (e.g., thermallytempered, heat bent and/or heat strengthened). Coated articles accordingto certain example embodiments of this invention may be used in thecontext of bent vehicle windshields or in any other suitableapplication.

BACKGROUND OF THE INVENTION

Coated articles are known in the art for use in window applications suchas insulating glass (IG) window units, vehicle windows, and/or the like.It is known that in certain instances, it is desirable to heat treat(e.g., thermally temper, heat bend and/or heat strengthen) such coatedarticles for purposes of tempering, bending, or the like in certainexample instances.

In certain situations, designers of coated articles often strive for acombination of high visible transmission, substantially neutral color,low emissivity (or emittance), and low sheet resistance (R_(s)). Highvisible transmission for example may permit coated articles to be moredesirable in certain window applications, whereas low-emissivity (low-E)and low sheet resistance characteristics permit such coated articles toblock significant amounts of IR radiation so as to reduce for exampleundesirable heating of vehicle or building interiors.

In applications such as vehicle windshields requiring a visibletransmission of at least 70%, or even at least 75%, the coated articlemust be bent as well as heat treated. The bending is often performed byallowing a coated glass article to sag while being heat treated in aknown manner. The heat treatment of such coated articles typicallyrequires the use of temperature(s) of at least 580 degrees C., morepreferably of at least about 600 degrees C. and often at least 620degrees C., for about 5–10 minutes or more.

Unfortunately, heretofore, too much bending often causes such coatedarticles to suffer damage known as mottling. Mottling defectsessentially result from cracking of the coating. With certain coatedarticles, mottling occurs when the coated article is heat bent to asignificant extent. It is believed that the mottling damage results fromhigh degrees of bending during heat treatment.

FIG. 1 is provided for the purpose of explaining the degree of bendingof a coated glass article such as a vehicle windshield. FIG. 1 is across sectional view of a bent vehicle windshield. Parameter “x” in FIG.1 represents the amount of bend in the windshield, and is known as acenterline convex value. The centerline convex value x is the distancebetween the apex of the interior surface of the windshield drawnstraight down to a line (see the dotted line in FIG. 1) connecting thetwo ends of the windshield. This centerline convex value x isrepresentative of the amount of bend (or depth of bend) in thewindshield; the higher the value x, the higher the amount of bend in thewindshield. FIG. 2 is a cross sectional view of a heat bent vehiclewindshield (e.g., of FIG. 1, or an embodiment herein) which includesfirst and second heat bent glass substrates laminated to one another viaa polymer inclusive layer (e.g., of or including PVB or any othersuitable polymer inclusive material) 42, where the low-E (lowemissivity) coating is provided on one of the substrates.

While many known windshields are capable of withstanding bends of about18 mm (i.e., a centerline convex value x of about 18 mm), they cannotwithstand bending to a greater extend without suffering from fatalmottling damage.

Consider the following coated article with the below-listed layer stack,where the layers are listed in order from the glass substrate outwardly.

Glass Substrate

TiO₂

Si₃N₄

ZnO

Ag

NiCrO_(x)

SnO₂

Si₃N₄

ZnO

Ag

NiCrO_(x)

SnO₂

Si₃N₄

While the aforesaid coated article is heat treatable, it cannotwithstand significant degrees of heat bending without suffering fatalmottling damage. For example, such a coated article suffers fatalmottling damage at centerline convex values x of about 22–23 mm or more(i.e., a bend about 22–23 mm or more deep). In this regard, it isbelieved that the mottling damage begins at the interface between thesilicon nitride and zinc oxide layers under the top silver layer, andthen expands through the coating.

It will be appreciated by those skilled in the art that there sometimesexists a need for a vehicle windshield which is bent to a significantextent (e.g., bent to a centerline convex value x of at least about 24mm, sometimes at least about 26 mm, or at least 28 mm, or even at least30 mm in certain situations). Unfortunately, the coated articlediscussed above cannot be used in such applications because it cannotwithstand such high degrees of bending without suffering fatal mottlingdamage.

Moreover, in vehicle windshield or other applications such as ininsulating glass (IG) window units, lengthy heat treatments at hightemperatures tend to cause the aforesaid coated article to suffersignificant drops in visible transmission, significant changes incertain color value(s), and significant increases in sheet resistance(R_(s)). Thus, there is room for improvement in one or more of theserespects. Additionally, the aforesaid coated article is susceptible toscratching in certain instances, and is also sometimes characterized byhigh haze values following heat treatment in certain instances.

In view of the above, it will be apparent to those skilled in the artthat there exists a need for coated articles which are capable of: (a)being bent to greater extents in applications such as vehiclewindshields or the like, (b) being able to maintain acceptable opticalcharacteristics when bent to such extents, (c) realizing improved orgood thermal stability with regard to visible transmission, color,emissivity (or emittance), and/or sheet resistance (R_(s)); (d)realizing improved mechanical durability such as scratch resistance;and/or (e) realizing improved haze characteristics. In certain exampleembodiments, it may be desired that one or more of these characteristicscan be achieved.

BRIEF SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

In certain example embodiments of this invention, an interlayercomprising tin oxide is provided under an infrared (IR) reflecting layerso as to be located between respective layers comprising silicon nitrideand zinc oxide.

Unexpectedly, it has been found that the use of such a tin oxideinclusive interlayer (or adhesion layer) results in significantlyimproved bendability of coated articles in applications such as vehiclewindshields or the like. In particular, it has surprisingly been foundthat the provision of such a tin oxide inclusive interlayer (or adhesionlayer) permits a coated article to be bent to a significantly greaterextent without suffering significant or fatal mottling damage in certainexample embodiments of this invention.

In certain example embodiments of this invention, coated articles withsuch a tin oxide inclusive interlayer can be heat bent to a centerlineconvex value “x” of at least about 24 mm, more preferably at least about26 mm, more preferably at least 28 mm, even more preferably at least 30mm, still more preferably at least about 32 mm, more preferably at leastabout 34 mm, and sometimes at least about 36 mm, without sufferingsignificant or fatal mottling damage.

In certain example embodiments of this invention, it is possible thatthe tin oxide inclusive interlayer can improve mechanical durability(e.g., scratch resistance) and/or haze characteristics in applicationssuch as vehicle windshields, IG window units, and/or the like.

These surprisingly results, which in certain example instances areassociated with the use of the combination layer stack portion of glass. . . Si_(x)N_(y)/SnO₂/ZnO/Ag . . . , are highly advantageous, sincereduction in mottling damage, bendability and/or improved scratchresistance are typically desired features in coated articles such asvehicle windows, IG window units, and/or the like.

In certain example instances, it has been found that the presence of thetin oxide inclusive interlayer in certain situations can result inthermal stability issues in vehicle windshield applications wheresignificant bending and heat treatment are performed (e.g., suitablevisible transmission cannot be maintained following heat treatment andbending). However, it has unexpectedly been found that the provision ofan overcoat layer of or including zirconium oxide or the like can reduceand/or eliminate such thermal stability problems. In particular, incertain example embodiments of this invention, the use of a zirconiumoxide inclusive overcoat layer in combination with the tin oxideinclusive interlayer can result in a coated article which does notsuffer from significant thermal stability issues (e.g., realizesacceptable visible transmission, a* and/or b* values following heattreatment and bending).

In certain example embodiments of this invention, there is provided abent vehicle windshield comprising first and second bent glasssubstrates, the first bent substrate supporting a coating thereon, thecoating comprising: a first dielectric layer supported by the first bentglass substrate; a first infrared (IR) reflecting layer comprisingsilver supported by the first bent glass substrate and located over atleast the first dielectric layer; a first layer comprising siliconnitride located over at least the first IR reflecting layer and thefirst dielectric layer; a first layer comprising tin oxide located overand contacting the first layer comprising silicon nitride; a first layercomprising zinc oxide located over and contacting the first layercomprising tin oxide, so that the first layer comprising tin oxide islocated between and contacting the first layer comprising siliconnitride and the first layer comprising zinc oxide; a second IRreflecting layer comprising silver located over and contacting the firstlayer comprising zinc oxide; and at least another dielectric layerlocated over at least the second IR reflecting layer.

In other example embodiments of this invention, there is provided aheated treated and bent coated article including a coating supported bya glass substrate, the coating comprising from the glass substrateoutwardly: first and second IR reflecting layers comprising silver; atleast one of said IR reflecting layers being provided directly on andcontacting a layer comprising zinc oxide, wherein said layer comprisingzinc oxide is located directly on and contacting a layer comprising tinoxide; and wherein the coated article is capable of being heat bent soas to have a centerline convex value “x” of at least about 26 mm, morepreferably at least about 28 mm, even more preferably at least about 30mm, without experiencing significant mottling damage due to heatbending.

In still further example embodiments of this invention, there isprovided a method of making a window, the method comprising: forming acoating on a glass substrate, the coating comprising first and secondlayers comprising silver with at least a layer comprising tin oxidetherebetween; and heat bending the glass substrate with the coatingthereon to an extent so as to have a centerline convex value “x” of atleast about 28 mm without experiencing significant mottling damage dueto the heat bending.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the centerline convex value(“x”) of a bent vehicle windshield or other bent coated article.

FIG. 2 is a cross sectional view of a bent vehicle windshield, of FIG.1, or of a suitable embodiment of this invention.

FIG. 3 is a cross sectional view of a coated article according to anexample embodiment of this invention.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION

Coated articles herein may be used in applications such as bent vehiclewindshields, other types of vehicle windows, and/or any other suitableapplication such as in an IG or monolithic window unit.

In certain example embodiments of this invention, an interlayercomprising tin oxide (e.g., see layer 15 in FIG. 3) is provided under aninfrared (IR) reflecting layer (e.g., see layer 19 in FIG. 3) so as tobe located between respective layers comprising silicon nitride and zincoxide. Unexpectedly, it has been found that the use of such a tin oxideinclusive interlayer (or adhesion layer) results in significantlyimproved bendability of coated articles in applications such as vehiclewindshields or the like. In particular, it has surprisingly been foundthat the provision of such a tin oxide inclusive interlayer (or adhesionlayer) permits a coated article to be bent to a significantly greaterextent without suffering significant or fatal mottling damage in certainexample embodiments of this invention.

In certain example embodiments of this invention, improved mechanicaldurability and/or reduced damage upon heat treatment can be realizedwhen thermodynamically stable silver based layers are deposited, and theuse of the tin oxide 15 is believed to aid in providing such silverbased layers even though the tin oxide 15 is not in direct contact withthe silver 19 in certain example embodiments of this invention. It isbelieved that the tin oxide 15 may reduce damage to the zinc oxide 17which may otherwise be caused by silicon nitride 14 directly contactingthe zinc oxide 17 if the tin oxide was not present. In other words, ithas unexpectedly been found that by providing a metal oxide (e.g., tinoxide) inclusive layer 15 between the silicon nitride 14 and zinc oxide17, significantly improved bendability can be achieved. It is believedthat the elimination of the silicon nitride/zinc oxide interface underthe top IR reflecting layer 19 leads to a more stable and heattreatable/bendable product.

In certain example embodiments of this invention, coated articles withsuch a tin oxide inclusive interlayer 15 can be heat bent to acenterline convex value “x” of at least about 24 mm (e.g., see FIG. 1),more preferably at least about 26 mm, more preferably at least about 28mm, even more preferably at least 30 mm, still more preferably at leastabout 32 mm, more preferably at least about 34 mm, and sometimes atleast about 36 mm, without suffering significant or fatal mottlingdamage. In certain example embodiments of this invention, it is possiblethat the tin oxide inclusive interlayer can also improve mechanicaldurability (e.g., scratch resistance) and/or haze characteristics inapplications such as vehicle windshields, IG window units, monolithicwindows, and/or the like.

These surprisingly results, which in certain example instances areassociated with the use of the combination layer stack portion of glass. . . Si_(x)N_(y)/SnO₂/ZnO/Ag . . . , are highly advantageous, sincereduction in mottling damage, bendability and/or improved scratchresistance are typically desired features in coated articles such asvehicle windows, IG window units, and/or the like.

In certain example instances, it has been found that the presence of thetin oxide inclusive interlayer in certain situations can result inthermal stability problems in vehicle windshield applications wheresignificant bending and heat treatment are performed (e.g., suitablevisible transmission cannot be maintained following heat treatment andbending). However, it has unexpectedly been found that the provision ofan overcoat layer of or including zirconium oxide (e.g., see layer 27 inFIG. 3) or the like can reduce and/or eliminate such thermal stabilityproblems. In particular, in certain example embodiments of thisinvention, the use of a zirconium oxide inclusive overcoat layer 27 incombination with the tin oxide inclusive interlayer 15 can result in acoated article which does not suffer from significant thermal stabilityissues (e.g., the coated article can realize acceptable visibletransmission, a* and/or b* values following heat treatment and bending).

Example advantages associated with certain example embodiments of thisinvention include a coated article which is capable of: (a) being bentto greater extents in applications such as vehicle windshields or thelike, (b) being able to maintain acceptable optical characteristics whenbent to such extents, (c) realizing improved or good thermal stabilitywith regard to visible transmission, color, emissivity (or emittance),and/or sheet resistance (R_(s)); (d) realizing improved mechanicaldurability such as scratch resistance; and/or (e) realizing improvedhaze characteristics. In certain example embodiments, one or more ofthese characteristics/advantages can be achieved.

In certain example embodiments of this invention, the coating includes adouble-silver stack, although this invention is not so limited in allinstances. For example, in certain example embodiments of thisinvention, heat treated and/or heat bent coated articles having multipleIR reflecting layers (e.g., two spaced apart silver based layers) arecapable of realizing a sheet resistance (R_(s)) of less than or equal to3.0 (more preferably less than or equal to 2.5, even more preferablyless than or equal to 2.1, and most preferably less than or equal to2.0). In certain example embodiments, following heat treatment and asmeasured in monolithic and/or laminated form, coated articles herein arecapable of realizing a visible transmission (Ill. C, 2 degree) of atleast about 70%, more preferably of at least about 75%, and mostpreferably of at least about 76%.

The terms “heat treatment” and “heat treating” as used herein meanheating the article to a temperature sufficient to achieve thermaltempering, heat bending, and/or heat strengthening of the glassinclusive coated article. This definition includes, for example, heatinga coated article in an oven or furnace at a temperature of least about580 degrees C., more preferably at least about 600 degrees C., for asufficient period to allow tempering, bending, and/or heatstrengthening. In certain instances, the HT may be for at least about 4or 5 minutes or more.

Bending may be performed in any suitable manner. For example, andwithout limitation, in forming a windshield including a pair of glasssubstrates, two flat glass substrates (at least one with a coatingthereon) can be placed in a bending furnace (e.g., on a bending mold) inan overlapping manner by interposing an optional lubricating powder suchas sodium hydrogen carbonate, cerite, magnesium oxide, silica, or thelike between contacting surfaces of the two glass substrates. The glasssubstrates are then heated using infrared (IR) emitting heating elementsto a processing temperature(s) near a softening point of the glass(e.g., from about 550 to 850 degrees C., more preferably from about 580to 750 degrees C.) in order to soften the overlapping glass substrates.Upon softening, the glass substrates (including any solar controlcoating such as a low-E coating thereon) are bent by their deadweight(i.e., sagging) along a shaping surface of a bending mold (not shown)into the desired curved shape appropriate for the vehicle windshieldbeing made. A press bending apparatus may optionally be used after theglass is sufficiently softened (e.g., press bending may be conducted asthe final step before cooling the glass). After being heat bent in sucha manner, the bent glass substrates (with solar control coating still onthe bent substrate) are separated from one another and a polymerinclusive interlayer sheet (e.g., PVB) is interposed therebetween. Thebent glass substrates are then laminated to one another via the polymerinclusive interlayer (e.g., PVB) in order to form the resulting vehiclewindshield.

FIG. 3 is a side cross sectional view of a coated article according toan example non-limiting embodiment of this invention. The coated articleincludes substrate 1 (e.g., clear, green, bronze, or blue-green glasssubstrate from about 1.0 to 10.0 mm thick, more preferably from about1.0 mm to 3.5 mm thick), and coating (or layer system) 30 provided onthe substrate 1 either directly or indirectly. The coating (or layersystem) 30 includes: bottom silicon nitride inclusive dielectric layer 3which may be Si₃N₄, of the Si-rich type for haze reduction, or of anyother suitable stoichiometry in different embodiments of this invention,first lower contact layer 7 (which contacts IR reflecting layer 9),first conductive and preferably metallic infrared (IR) reflecting layer9, first upper contact layer 11 (which contacts layer 9), dielectriclayer 13 (which may be deposited in one or multiple steps in differentembodiments of this invention) of or including tin oxide, anothersilicon nitride inclusive layer 14, tin oxide inclusive interlayer (oradhesion layer) 15, second lower contact layer 17 (which contacts IRreflecting layer 19), second conductive and preferably metallic IRreflecting layer 19, second upper contact layer 21 (which contacts layer19), dielectric layer 23, and silicon nitride inclusive layer 25, andfinally optional protective dielectric layer 27 of or includingzirconium oxide. The “contact” layers 7, 11, 17 and 21 each contact atleast one IR reflecting layer (e.g., layer based on Ag). The aforesaidlayers 2–27 make up low-E (i.e., low emissivity) coating 30 which isprovided on glass or plastic substrate 1.

In monolithic instances, the coated article includes only one glasssubstrate 1 as illustrated in FIG. 1. However, monolithic coatedarticles herein may be used in devices such as laminated vehiclewindshields, IG window units, and the like. As shown in FIG. 2, alaminated vehicle window such as a windshield typically includes firstand second glass substrates 1 and 40 laminated to one another via apolymer based interlayer 42 (e.g., see U.S. Pat. No. 6,686,050, thedisclosure of which is incorporated herein by reference). One of thesesubstrates of the laminate may support coating 30 on an interior surfacethereof in certain example embodiments (either substrate may support thelow-E coating 30, although the inner substrate supports the coating inthe example shown in FIG. 2). As for IG window units, an IG window unitmay include two spaced apart substrates. An example IG window unit isillustrated and described, for example, in U.S. Pat. No. 6,632,491, thedisclosure of which is hereby incorporated herein by reference. Anexample IG window unit may include, for example, the coated glasssubstrate 1 shown in FIG. 3 coupled to another glass substrate viaspacer(s), sealant(s) or the like with a gap being defined therebetween.This gap between the substrates in IG unit embodiments may in certaininstances be filled with a gas such as argon (Ar).

Dielectric layers 3 and 14 may be of or include silicon nitride incertain embodiments of this invention. Silicon nitride layers 3 and 14may, among other things, improve heat-treatability of the coatedarticles, e.g., such as thermal tempering or the like. The siliconnitride of layers 3 and/or 14 may be of the stoichiometric type (i.e.,Si₃N₄), or alternatively of the Si-rich type in different embodiments ofthis invention. For example, Si-rich silicon nitride 3 (and/or 14)combined with zinc oxide and/or tin oxide under a silver based IRreflecting layer may permit the silver to be deposited (e.g., viasputtering or the like) in a manner which causes its sheet resistance tobe lessened compared to if certain other material(s) were under thesilver. Moreover, the presence of free Si in a Si-rich silicon nitrideinclusive layer 3 may allow certain atoms such as sodium (Na) whichmigrate outwardly from the glass 1 during heat treatment (HT) to be moreefficiently stopped by the Si-rich silicon nitride inclusive layerbefore they can reach the silver and damage the same. Thus, it isbelieved that the oxidation caused by heat treatment allows visibletransmission to increase, and that the Si-rich Si_(x)N_(y) in layer 3for example can reduce the amount of damage done to the silver layer(s)during HT in certain example embodiments of this invention therebyallowing sheet resistance (R_(s)) to decrease or remain about the samein a satisfactory manner.

In certain example embodiments, when Si-rich silicon nitride us used inlayer 3 and/or 14, the Si-rich silicon nitride layer as deposited may becharacterized by Si_(x)N_(y) layer(s), where x/y may be from 0.76 to1.5, more preferably from 0.8 to 1.4, still more preferably from 0.85 to1.2. Moreover, in certain example embodiments, before and/or after HTthe Si-rich Si_(x)N_(y) layer(s) may have an index of refraction “n” ofat least 2.05, more preferably of at least 2.07, and sometimes at least2.10 (e.g., 632 nm) (note: stoichiometric Si₃N₄ which may also be usedhas an index “n” of 2.02–2.04). In certain example embodiments, it hassurprisingly been found that improved thermal stability is especiallyrealizable when the Si-rich Si_(x)N_(y) layer(s) as deposited has anindex of refraction “n” of at least 2.10, more preferably of at least2.20, and most preferably from 2.2 to 2.4. Also, the Si-rich Si_(x)N_(y)layer in certain example embodiments may have an extinction coefficient“k” of at least 0.001, more preferably of at least 0.003 (note:stoichiometric Si₃N₄ has an extinction coefficient “k” of effectively0). Again, in certain example embodiments, it has surprisingly beenfound that improved thermal stability can be realized when “k” for theSi-rich Si_(x)N_(y) layer(s) is from 0.001 to 0.05 as deposited (550nm). It is noted that n and k tend to drop due to heat treatment.

Any and/or all of the silicon nitride layers discussed herein may bedoped with other materials such as stainless steel or aluminum incertain example embodiments of this invention. For example, any and/orall silicon nitride layers discussed herein may optionally include fromabout 0–15% aluminum, more preferably from about 1 to 10% aluminum, incertain example embodiments of this invention. The silicon nitride maybe deposited by sputtering a target of Si or SiAl in an atmosphereincluding at least nitrogen gas in certain embodiments of thisinvention.

Infrared (IR) reflecting layers 9 and 19 are preferably substantially orentirely metallic and/or conductive, and may comprise or consistessentially of silver (Ag), gold, or any other suitable IR reflectingmaterial. IR reflecting layers 9 and 19 help allow the coating to havelow-E and/or good solar control characteristics. The IR reflectinglayers may, however, be slightly oxidized in certain embodiments of thisinvention.

The upper contact layers 11 and 21 may be of or include nickel (Ni)oxide, chromium/chrome (Cr) oxide, or a nickel alloy oxide such asnickel chrome oxide (NiCrO_(x)), or other suitable material(s), incertain example embodiments of this invention. The use of, for example,NiCrO_(x) in these layers (11 and/or 21) allows durability to beimproved. The NiCrO_(x) of layers 11 and/or 21 may be fully oxidized incertain embodiments of this invention (i.e., fully stoichiometric), oralternatively may only be partially oxidized (i.e., sub-oxide). Incertain instances, the NiCrO_(x) layers 11 and/or 21 may be at leastabout 50% oxidized. Contact layers 11 and/or 21 (e.g., of or includingan oxide of Ni and/or Cr) may or may not be oxidation graded indifferent embodiments of this invention. Oxidation grading means thatthe degree of oxidation in the layer changes throughout the thickness ofthe layer. For example, a contact layer 11 and/or 21 may be graded so asto be less oxidized at the contact interface with the immediatelyadjacent IR reflecting layer than at a portion of the contact layer(s)further or more/most distant from the immediately adjacent IR reflectinglayer. Descriptions of various types of oxidation graded contact layersare set forth in U.S. Pat. No. 6,576,349, the disclosure of which ishereby incorporated herein by reference. Contact layers 11 and/or 21(e.g., of or including an oxide of Ni and/or Cr) may or may not becontinuous in different embodiments of this invention across the entireunderlying IR reflecting layer.

Dielectric layer 13 may be of or include tin oxide in certain exampleembodiments of this invention. However, as with other layers herein,other materials may be used in different instances.

Lower contact layers 7 and/or 17 in certain embodiments of thisinvention are of or include zinc oxide (e.g., ZnO). The zinc oxide oflayers 7 and 17 may contain other materials as well such as Al (e.g., toform ZnAlO_(x)). For example, in certain example embodiments of thisinvention, one or more of zinc oxide layers 7, 17 may be doped with fromabout 1 to 10% Al, more preferably from about 1 to 5% Al, and mostpreferably about 1 to 4% Al.

Interlayer 15 of or including tin oxide is provided under IR reflectinglayer 19 so as to be located between silicon nitride layer 14 and zincoxide layer 17. Surprisingly, as explained above, it has been found thatthe use of such a tin oxide inclusive interlayer 15 results insignificantly improved bendability of coated articles in applicationssuch as vehicle windshields or the like. In particular, it hassurprisingly been found that the provision of such a tin oxide inclusiveinterlayer 15 permits a coated article to be bent to a significantlygreater extent without suffering significant or fatal mottling damage incertain example embodiments of this invention. The presence of thislayer also surprisingly improves scratch resistance in certain exampleinstances. In certain alternative embodiments, it is possible to dopethe tin oxide of layer 15 with other materials such as Al, Zn, N, or thelike. Alternatively, other metal oxide(s) may be used for layer 15 incertain instances.

Dielectric layer 23 may be of or include tin oxide in certain exampleembodiments of this invention. However, layer 23 is optional and neednot be provided in certain example embodiments of this invention.Dielectric layer 25 may be of or include silicon nitride (e.g., Si₃N₄)or any other suitable material in certain example embodiments of thisinvention. Optionally, other layers may be provided above layer 25.Layer 25 is provided for durability purposes, and to protect theunderlying layers during heat treatment and/or environmental use. Incertain example embodiments, layer 25 may have an index of refraction(n) of from about 1.9 to 2.2, more preferably from about 1.95 to 2.05.

In highly bent windshield applications, it has been found that thepresence of the tin oxide inclusive interlayer 15 in certain situationscan result in thermal stability problems when significant bending andheat treatment are performed (e.g., suitable visible transmission cannotbe maintained following heat treatment and bending). However, it hasunexpectedly been found that the provision of an overcoat layer 27 of orincluding zirconium oxide can reduce and/or eliminate such thermalstability issues. In particular, in certain example embodiments of thisinvention, the use of a zirconium oxide inclusive overcoat layer 27 incombination with the tin oxide inclusive interlayer 15 can result in acoated article which can be significantly heat bent without sufferingfrom fatal mottling damage and which does not suffer from significantthermal stability issues (e.g., the coated article can realizeacceptable visible transmission, a* and/or b* values following heattreatment and bending).

For purposes of example, first and second coated articles were made soas to have essentially the same layer stack as shown in FIG. 3, exceptthat the second stack did not include a zirconium oxide overcoat layer27. After heat treatment in a box furnace at 695 degrees C. and bending,the coated article with the zirconium oxide overcoat layer 27 hadsignificantly higher visible transmission than did the coated articlewithout the zirconium oxide overcoat layer heat treated in the samemanner (over 2% higher). This illustrates that, unexpectedly, theprovision of the metal oxide overcoat layer (e.g., zirconium oxide layer27) significantly increase the visible transmission of the coatedarticle following HT. In certain example embodiments, the index “n” ofthe zirconium oxide layer 27 is from about 2.1 to 2.25, more preferablyabout 2.16 (at 550 nm).

It has also been found that thinning the top silicon nitride layer 25 isalso surprisingly advantageous (e.g., to a thickness of no greater thanabout 100 Å). In particular, the combination of adding the tin oxideinclusive layer 15 and thinning the top silicon nitride layer 25 to athickness no greater than about 100 Å had the effect of eliminating orsignificantly reducing the aforesaid mottling problem in high bendapplications. Thus, it is believed that thinning of the silicon nitridelayer 25 also contributes to eliminating or reducing the mottlingproblem. However, the thinning of the top silicon nitride inclusivelayer 25 and the insertion of the tin oxide layer 15 to reduce mottlingmay tend to create some thermal stability problems. In this respect, themetal oxide (e.g., zirconium oxide) overcoat layer 27 has been added toimprove thermal stability as discussed above.

In certain example embodiments, it has been found that good opticalproperties are achieved when the total thickness of the combination oftin oxide inclusive layers 13 and 15 is from about 500 to 800 Å, morepreferably from about 600 to 700 Å. This total thickness of thecombination of layers 13 and 15 may be divided up in any suitable mannerin certain example embodiments of this invention. Moreover, the totalthickness of layers 3 and 7 may be from about 200 to 400 Å in certainexample embodiments of this invention, more preferably from about 220 to350 Å; and the total thickness of layers 23, 25 and 27 may be from about300 to 500 Å in certain example embodiments.

Other layer(s) below or above the illustrated coating may also beprovided. Thus, while the layer system or coating is “on” or “supportedby” substrate 1 (directly or indirectly), other layer(s) may be providedtherebetween. Thus, for example, the coating of FIG. 3 may be considered“on” and “supported by” the substrate 1 even if other layer(s) areprovided between layer 3 and substrate 1. Moreover, certain layers ofthe illustrated coating may be removed in certain embodiments, whileothers may be added between the various layers or the various layer(s)may be split with other layer(s) added between the split sections inother embodiments of this invention without departing from the overallspirit of certain embodiments of this invention.

While various thicknesses and materials may be used in layers indifferent embodiments of this invention, example thicknesses andmaterials for the respective layers on the glass substrate 1 in the FIG.3 embodiment are as follows, from the glass substrate outwardly:

Example Materials/Thicknesses; FIG. 3 Embodiment Layer Preferred MorePreferred Glass (1–10 mm thick) Range ({acute over (Å)}) ({acute over(Å)}) Example (Å) Si_(x)N_(y) (layer 3)  40–450 Å  70–300 Å 186 ÅZnO_(x) (layer 7)  10–300 {acute over (Å)}  40–150 {acute over (Å)} 107Å Ag (layer 9)  50–250 {acute over (Å)}  80–120 {acute over (Å)} 107 ÅNiCrO_(x) (layer 11)  10–100 {acute over (Å)}  12–40 {acute over (Å)} 30 Å SnO₂ (layer 13) 0–1,000 Å 200–700 Å 412 Å Si_(x)N_(y) (layer 14) 50–450 {acute over (Å)}  80–200 {acute over (Å)} 131 Å SnO₂ (layer 15) 30–250 Å  50–200 Å 108 Å ZnO_(x) (layer 17)  10–300 {acute over (Å)} 40–150 {acute over (Å)} 119 Å Ag (layer 19)  50–250 {acute over (Å)} 80–220 {acute over (Å)} 103 Å NiCrO_(x) (layer 21)  10–100 {acute over(Å)}  20–45 {acute over (Å)}  33 Å SnO₂ (layer 23)   0–750 Å  40–400 Å337 Å Si₃N₄ (layer 25)  10–750 {acute over (Å)}  20–100 {acute over (Å)} 53 Å ZrO_(x) (layer 27)   0–200 Å  10–50 Å  22 Å

In certain example embodiments of this invention, coated articles hereinmay have the following optical and solar characteristics set forth inTable 2 when measured monolithically (before any optional HT). The sheetresistances (R_(s)) herein take into account all IR reflecting layers(e.g., silver layers 9, 19).

Optical/Solar Characteristics (Monolithic; pre-HT) CharacteristicGeneral More Preferred Most Preferred R_(s) (ohms/sq.): <=5.0 <=4.0<=3.0 E_(n): <=0.07 <=0.04 <=0.03 T_(vis) (Ill. C 2°): >=70% >=75% >=77%

In certain example embodiments, coated articles herein may have thefollowing characteristics, measured monolithically for example, afterheat treatment (HT):

Optical/Solar Characteristics (Monolithic; post-HT) CharacteristicGeneral More Preferred Most Preferred R_(s) (ohms/sq.): <=3.0 <=2.5<=2.1 (or <=2.0) E_(n): <=0.07 <=0.04 <=0.03 T_(vis) (Ill. C2°): >=75% >=78% >=80% Transmitted Haze: <=0.5 <=0.4 <=0.38

Moreover, in certain example laminated embodiments of this invention,coated articles herein which have been heat treated to an extendsufficient for tempering (and optionally heat bent), and which have beenlaminated (via index oil and/or a polymer inclusive interlayer) toanother glass substrate may have the following optical/solarcharacteristics.

Example Optical Characteristics (Laminated: post-HT) CharacteristicGeneral More Preferred T_(vis) (or TY)(Ill. C 2°): >=70% >=75% a*_(t)(Ill. C 2°): −6 to +1.0 −5 to 0.0 b*_(t) (Ill. C 2°): −2.0 to +8.0 0.0to 6.0 L* (Ill. C 2°): 80–95 88–95 R_(f)Y (Ill. C, 2 deg.): 1 to 13% 1to 12% a*_(f) (Ill. C, 2°): −5.0 to +2.0 −4.0 to +0.5 b*_(f) (Ill. C,2°): −14.0 to +10.0 −10.0 to +3.5 L* (Ill. C 2°): 30–45 33–41 R_(g)Y(Ill. C, 2 deg.): 1 to 12% 1 to 10% a*_(g) (Ill. C, 2°): −5.0 to +3.0−2.5 to +2.5 b*_(g) (Ill. C, 2°): −20.0 to +10.0 −15.0 to 0 L* (Ill. C2°): 30–40 33–38 Haze (transmissive): <=0.6 <=0.5

The following examples are provided for purposes of example only, andare not intended to be limiting unless specifically claimed.

EXAMPLES

The following Examples were made via sputtering on a 2.1 mm thick clearglass substrate 1 so as to have approximately the layer stack set forthbelow. Example 1 is according to an example embodiment of this inventionas shown in FIG. 3. The thicknesses are in units of angstroms (Å) andare approximations.

Layer Glass Substrate Example 1 Si_(x)N_(y) 186 ZnO 107 Ag 107 NiCrO_(x)30 SnO₂ 412 Si_(x)N_(y) 131 SnO₂ 108 ZnO 119 Ag 103 NiCrO_(x) 33 SnO₂337 Si₃N₄ 53 ZrO 22

After being sputter deposited onto the glass substrates, the Examplecoated articles were heat treated in a manner sufficient for tempering.After being formed, the coated article of Example 1 was heat treated inan 8-zone belt furnace for 24 minutes. The eight zones of the beltfurnace were at the following temperatures in the following order: 480,520, 550, 600, 630, 660, 670 and 675 degrees C. (the coated articles wasin each zone for about three minutes during the HT). The coated articlehad the following characteristics, measured monolithically before andafter HT.

Example 1 Monolithic, Before/After HT

Characteristic pre-HT Post-HT T_(vis) (or TY)(Ill. C 2°): 77.64% 81.32%a*_(t) (Ill. C 2°): −5.05 −3.83 b*_(t) (Ill. C 2°): 5.36 1.03 R_(f)Y(Ill. C, 2 deg.): 6.03% 6.86% a*_(f) (Ill. C, 2°): 10.93 6.12 b*_(f)(Ill. C, 2°): 0.77 6.37 L* (Ill. C 2°): 29.49 31.48 R_(g)Y (Ill. C, 2deg.): 7.23% 7.69% a*_(g) (Ill. C, 2°): 16.28 12.66 b*_(g) (Ill. C, 2°):−8.09 −1.29 L* (Ill. C 2°): 32.33 33.33 R_(s) (ohms/square): 2.7 2.0Haze: n/a 0.31

Then, following lamination to another 2.1 mm clear glass substrate withindex oil, the coated article of Example 1 had the followingcharacteristics:

Example 1 Laminated, Post-HT

Characteristic Example 1 T_(vis) (or TY)(Ill. C 2°): 78.6% a*_(t) (Ill.C 2°): −3.17 b*_(t) (Ill. C 2°): 4.25 R_(f)Y (Ill. C, 2 deg.): 9.09%a*_(f) (Ill. C, 2°): −1.10 b*_(f) (Ill. C, 2°): −9.38 L* (Ill. C 2°):36.15 R_(g)Y (Ill. C, 2 deg.): 9.25% a*_(g) (Ill. C, 2°): 1.52 b*_(g)(Ill. C, 2°): −11.42 L* (Ill. C 2°): 36.47 R_(s) (ohms/square): 2.0 Haze(average): n/a

Moreover, heat bending of coated articles with the structure of Example1 to a centerline convex value “x” of 30 mm did not result in anysignificant mottling damage. For purposes of comparison, a similarcoated article except without a tin oxide layer 15 suffered fatalmottling damage once the bending reached a centerline convex value “x”of about 22–23 mm. Thus, is can be seen that the provision of the tinoxide layer 15 unexpectedly and significantly improves the bendabilityof the coated article.

Example 2 had the same layer stack as Example 1, except that it was heattreated and heat bent at a windshield manufacturing facility. The databelow for Example 2 is broken down into two parts, the first “afterbent” data being post-HT in monolithic form following being heat bentduring heat treatment to achieve a centerline convex value “x” of about30 mm (but before lamination), and the “laminated” data being post-HT(and post-bending) after being laminated to another bent glass substrate40 with a PVB layer 42 to form a windshield. The data below is based onthe average of data taken from two points, one in the center of thewindshield and the other at the edge (Ill. C, 2 degree). Example 2(post-HT—Bent to x=30 mm)

Characteristic After Bent Laminated T_(vis) (or TY)(Ill. C 2°): 79.95%77.02% a*_(t) (Ill. C 2°): −4.19 −4.77 b*_(t) (Ill. C 2°): 0.36 3.95R_(outside)Y (Ill. C, 2 deg.):  6.8%  8.57% a* (Ill. C, 2°): 7.59 2.76b* (Ill. C, 2°): 1.9 −8.5 R_(inside)Y (Ill. C, 2 deg.):  7.95%  9.04% a*(Ill. C, 2°): 12.64 4.45 b* (Ill. C, 2°): −1.5 −10.26

Moreover, heat bending of the Example 2 coated article to a centerlineconvex value “x” of 30 mm did not result in any significant mottlingdamage. Again, for purposes of comparison, a similar coated articleexcept without a tin oxide layer 15 suffered fatal mottling damage oncethe bending reached a centerline convex value “x” of about 22–23 mm.Thus, is can be seen that the provision of the tin oxide layer 15unexpectedly and significantly improves the bendability of the coatedarticle. The coated article of Example 2, in laminated, bent and thusheat treated form, showed excellent heat stability, color uniformity, nomottling damage, excellent cosmetics and optics in a finished windshieldproduct with a centerline convex value “x” of 30 mm.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A bent vehicle windshield comprising first and second bent glasssubstrates, the first bent substrate supporting a coating thereon, thecoating comprising: a first dielectric layer supported by the first bentglass substrate; a first infrared (IR) reflecting layer comprisingsilver supported by the first bent glass substrate and located over atleast the first dielectric layer; a first layer comprising siliconnitride located over at least the first IR reflecting layer and thefirst dielectric layer; a first layer comprising tin oxide located overand contacting the first layer comprising silicon nitride; a first layercomprising zinc oxide located over and contacting the first layercomprising tin oxide, so that the first layer comprising tin oxide islocated between and contacting the first layer comprising siliconnitride and the first layer comprising zinc oxide; a second IRreflecting layer comprising silver located over and contacting the firstlayer comprising zinc oxide; at least another dielectric layer locatedover at least the second IR reflecting layer; and wherein the windshieldis bent to a degree sufficient so as to have a centerline convex value“x” of at least about 26 mm.
 2. The windshield of claim 1, furthercomprising a second layer comprising zinc oxide that is located underand contacting the first IR reflecting layer, and wherein at least oneof the first and second layers comprising zinc oxide further comprisesaluminum.
 3. A bent vehicle windshield comprising first and second bentglass substrates, the first bent substrate supporting a coating thereon,the coating comprising: a first dielectric layer supported by the firstbent glass substrate; a first infrared (IR) reflecting layer comprisingsilver supported by the first bent glass substrate and located over atleast the first dielectric layer; a first layer comprising siliconnitride located over at least the first IR reflecting layer and thefirst dielectric layer; a first layer comprising tin oxide located overand contacting the first layer comprising silicon nitride; a first layercomprising zinc oxide located over and contacting the first layercomprising tin oxide, so that the first layer comprising tin oxide islocated between and contacting the first layer comprising siliconnitride and the first layer comprising zinc oxide; a second IRreflecting layer comprising silver located over and contacting the firstlayer comprising zinc oxide; at least another dielectric layer locatedover at least the second IR reflecting layer; and an overcoat layer ofzirconium oxide.
 4. A bent vehicle windshield comprising first andsecond bent glass substrates, the first bent substrate supporting acoating thereon, the coating comprising: a first dielectric layersupported by the first bent glass substrate; a first infrared (IR)reflecting layer comprising silver supported by the first bent glasssubstrate and located over at least the first dielectric layer; a firstlayer comprising silicon nitride located over at least the first IRreflecting layer and the first dielectric layer; a first layercomprising tin oxide located over and contacting the first layercomprising silicon nitride; a first layer comprising zinc oxide locatedover and contacting the first layer comprising tin oxide, so that thefirst layer comprising tin oxide is located between and contacting thefirst layer comprising silicon nitride and the first layer comprisingzinc oxide; a second IR reflecting layer comprising silver located overand contacting the first layer comprising zinc oxide; at least anotherdielectric layer located over at least the second IR reflecting layer;and a second layer comprising tin oxide located under and contacting thefirst layer comprising silicon nitride.
 5. The windshield of claim 1,wherein the first dielectric layer comprises silicon nitride, andwherein the windshield is substantially free of mottling.
 6. Thewindshield of claim 1, wherein the first dielectric layer comprisessilicon nitride, and said another dielectric layer also comprisessilicon nitride.
 7. The windshield of claim 1, wherein the first layercomprising silicon nitride is Si-rich so as to be represented bySi_(x)N_(y), where x/y is from 0.8 to 1.4.
 8. The windshield of claim 1,wherein the windshield following heat treatment has a visibletransmission of at least 75% and a sheet resistance (R_(s)) of less thanor equal to 3.0 ohms/square.
 9. The windshield of claim 1, wherein thewindshield is bent to a degree sufficient so as to have a centerlineconvex value “x” of at least about 28 mm.
 10. The windshield of claim 1,wherein the windshield is bent to a degree sufficient so as to have acenterline convex value “x” of at least about 30 mm.
 11. The windshieldof claim 4, wherein the windshield is bent to a degree sufficient so asto have a centerline convex value “x” of at least about 26 mm.
 12. Thewindshield of claim 3, wherein the coated article is heat treated and isbent to a degree sufficient so as to have a centerline convex value “x”of at least about 26 mm.
 13. A coated article comprising a coatingsupported by a bent glass substrate, the coating comprising from thebent glass substrate outwardly: a layer comprising silicon nitride; alayer comprising tin oxide located over and contacting the layercomprising silicon nitride; a layer comprising zinc oxide located overand contacting the layer comprising tin oxide, so that the layercomprising tin oxide is located between and contacting the layercomprising silicon nitride and the layer comprising zinc oxide; aninfrared (IR) reflecting layer located over and contacting the layercomprising zinc oxide; at least another dielectric layer located over atleast the IR reflecting; and wherein the coated article is heat treatedand is bent to a degree sufficient so as to have a centerline convexvalue “x” of at least about 26 mm.
 14. The coated article of claim 13,further comprising another IR reflecting layer and another layercomprising zinc oxide, wherein the another IR reflecting layer islocated directly on and contacting the another layer comprising zincoxide, wherein the another IR reflecting layer and the another layercomprising zinc oxide are located below the IR reflecting layer recitedin claim
 12. 15. The coated article of claim 13, wherein the coatedarticle is heat treated and is bent to a degree sufficient so as to havea centerline convex value “x” of at least about 28 mm.
 16. The coatedarticle of claim 13, wherein the coated article is heat treated and isbent to a degree sufficient so as to have a centerline convex value “x”of at least about 30 mm.
 17. The coated article of claim 13, wherein thecoated article is heat treated and is bent to a degree sufficient so asto have a centerline convex value “x” of at least about 32 mm.
 18. Thecoated article of claim 13, further comprising another layer comprisingtin oxide located under and contacting the layer comprising siliconnitride.
 19. The coated article of claim 13, wherein said at leastanother dielectric layer comprises at least one of silicon nitride andtin oxide.
 20. The coated article of claim 13, wherein the layercomprising silicon nitride is Si-rich so as to be represented bySi_(x)N_(y), where x/y is from 0.8 to 1.4.
 21. The coated article ofclaim 13, wherein the coated article comprises a vehicle windshieldwhich has a visible transmission of at least about 75% and a sheetresistance (R_(s)) of less than or equal to 3.0 ohms/square.
 22. Aheated treated and bent coated article including a coating supported bya glass substrate, the coating comprising from the glass substrateoutwardly: at least a first IR reflecting layer comprising silver; saidfirst IR reflecting layer being provided directly on and contacting alayer comprising zinc oxide, wherein said layer comprising zinc oxide islocated directly on and contacting a layer comprising tin oxide; andwherein the coated article is heat treated and is bent to a degreesufficient so as to have a centerline convex value “x” of at least about26 mm.
 23. The coated article of claim 22, wherein the coated article isbent so as to have a centerline convex value “x” of at least about 28 mmwithout experiencing significant mottling damage due to heat bending.24. The coated article of claim 22, wherein the coated article iscapable of being heat bent so as to have a centerline convex value “x”of at least about 30 mm without experiencing significant mottling damagedue to heat bending.
 25. The coated article of claim 22, wherein thecoated article has a visible transmission of at least about 75% and asheet resistance (R_(s)) of less than or equal to 3.0 ohms/square.
 26. Abent vehicle windshield comprising: a coating supported by a bent glasssubstrate, wherein the coating comprises first and second IR reflectinglayers comprising silver which are spaced apart from one another by atleast one layer comprising tin oxide, and wherein the windshield is bentto a degree sufficient so as to have a centerline convex value “x” of atleast about 26 mm.
 27. The coated article of claim 26, wherein thecoated article is capable of being heat bent so as to have a centerlineconvex value “x” of at least about 28 mm without experiencingsignificant mottling damage due to heat bending.
 28. The coated articleof claim 26, wherein the coated article is capable of being heat bent soas to have a centerline convex value “x” of at least about 30 mm withoutexperiencing significant mottling damage due to heat bending.
 29. Thecoated article of claim 26, wherein the coated article has a visibletransmission of at least about 75% and a sheet resistance (R_(s)) ofless than or equal to 3.0 ohms/square.
 30. The coated article of claim22, further comprising a second IR reflecting layer comprising silverthat is located between at least the glass substrate and the first IRreflecting layer.